(1) Field of the Invention
The present invention relates to a control system including means to steer conveyor carts for carrying various articles in a factory or warehouse.
More particularly, the invention relates to a control system comprising conveyor carts and magnetic guiding lines extending along running tracks. Each conveyor cart includes detecting means for detecting the guiding lines and outputting detection data for use in steering control, and steering control means operable in response to the detection data for causing the cart to run automatically along the guiding lines.
(2) Description of the Prior Art
With this type of running control system, it has been conventional practice to derive, from detection data provided by magnetism sensing means, a displacement of the conveyor cart with respect to the centerline of the guiding line and to steer the cart to decrease the displacement with respect to the centerline to zero (see Japanese utility model publication No. 51-47196 for example).
This type of running control system includes the cases of causing the conveyor cart to run along a running track branching from another and to run along a running track merging with another. In the prior art, however, the cart is caused to run along the guiding line following its centerline, and therefore the cart is unable to run along a branching or merging line as desired where guiding lines are installed along two running tracks. More particularly, the magnetism detecting means detects the two guiding lines at a branching or merging point at the same time. As a result, the centerline of a target guiding line branching from or merging with another line cannot be detected accurately, and the cart tends to run into trouble such as a deviation from the selected running track.
The conveyor cart may be allowed to run by self-control at the branching or merging section on the basis of pre-stored steering data without using the detection data provided by the magnetism detecting means. However, this control mode has disadvantages from a practical point of view in that the construction for effecting the steering control is complicated and that the conveyor cart could slip off a selected running track.
There is another known running control system which includes magnetic guiding lines along running tracks and magnetism detecting means (sensor) having a plurality of magnetism sensitive elements arrange transversely of a conveyor cart. According to this system, transverse displacements of the cart relative to the guiding line are detected in a plurality of steps on the basis of data as to which magnetism sensitive elements are detecting the magnetism of the guiding line. The plurality of magnetism sensitive elements provide detection signals which are input to a control unit in parallel. Thus, the control unit scans the magnetism sensitive elements sequentially from an element at one end, and judges order numbers of the operating elements counted from the center of the sensor. Then the voltage is changed to correspond to the positions of the operating elements, thereby deriving a signal corresponding to the transverse displacement of the cart relative to the guiding line (See the Japanese patent application laid open under No. 59-154511).
The above known construction requires the operation for causing the plurality of magnetism sensitive elements to output their respective detection signals in parallel, scanning the elements sequentially to determine the positions of operating elements, and changing the voltage signal to correspond to the displacement in response to the positions of operating elements. This construction requires a great number of connecting wires between the control unit and sensor, and its displacement detecting operation is complicated.
The construction in which the plurality of magnetism sensitive elements are scanned sequentially from one end to find operating elements, requires a great number of wires between the sensor and control unit if the number of magnetism sensitive elements is increased in order to improve resolution of the detection signals. This necessitates a troublesome wiring operation and increases the chances of miswiring. Furthermore, one scan of all the magnetism sensitive elements takes a long time, which means that a long time is required for detecting the displacement of the conveyor cart relative to the guiding line. Therefore, the above construction has the disadvantage of slow response for steering the cart.